In the field of industrial packaging, bundles of articles or loose materials are sometimes wrapped with metal tying wire applied by automatic machines which twist the wire into a knot to secure the bundle. The wire itself and the knot must meet certain strength requirements such as those specified by the American Association of Railroads (AAR) which require an ultimate tensile strength of at least 1275 pounds for 12 gage, 0.106 inch diameter Grade 145 wire and a knot joint strength when pulled in tension of 1080 pounds. To meet the AAR limits, a drawn round steel wire of AISI 1055 or 1065 composition may be supplied in the sub-critical annealed condition to provide wire ultimate tensile strength of at least 1275 pounds.
In prior art practice, the wire is coated with zinc applied by a hot dip process. The pure zinc outer layer is wiped off with asbestos wipes to leave an iron-zinc alloy coating which provides a good non-slip surface so that knots formed in the wire will meet the knot joint strength requirement. However, even with wiping, a relatively thick zinc layer is inherently formed in the hot-dip coating process. Consequently the wire has excellent corrosion resistance, better than is necessary for the application since moderate rusting may be tolerated after the wire is applied to the bundle. Thus, one disadvantage of the hot-dip galvanized product is that an excess of zinc is inherently used, increasing the cost of the product.
Another disadvantage lies in the fact that the wire must be cleaned prior to hot-dip galvanizing in order to remove drawing lubricant or other material which might prevent obtaining a uniform coating. Acid cleaning is normally used to clean the wire and causes additional expenses for disposal of used acids.